1. Field of the Invention
The present invention relates to a tape drive capstan motor assembly for moving a tape within a tape cartridge, and more particularly to a capstan motor assembly including an intermeshing gear train for transmitting motor torque from the motor to the tape driver without slippage between the elements.
2. Description of the Related Art
Tape drives are widely used in data processing systems for applications including primary data storage, archival data storage, journaling, and most significantly, as a back-up data storage device to the system's hard drive. Conventional tape drives are designed to transfer data to and from a length of magnetically encoded tape, typically one-quarter inch in width, which tape is transferred between a supply reel and a take-up reel. Currently, most 31/2 inch form factor tape drives utilize a so called "minicartridge" cassette tape for data storage. This type of cartridge is generally described in American National Standard ANSI 3.55-1977.
In conventional tape drive operation, as shown in FIG. 1, the data tape 10 within the cartridge 12 travels from a supply reel 13, past a front face of the cartridge, and is stored on a take-up reel 14. The tape is advanced between the take-up and supply reels by means of a belt 16 within the cartridge. The belt is wrapped around a capstan belt wheel 17 within the cassette which is driven by a capstan motor assembly 18 within the tape drive.
As shown in FIG. 1, a conventional capstan motor assembly 18 includes a capstan drive roller 20 rotatably engaging an idler 22. Idler 22 is small enough so that a portion of the idler may be received through the opening 29 in the front face of cartridge 12 to thereby contact the capstan belt wheel 17 within the cartridge 12. When the cartridge 12 is properly inserted within the drive, the capstan belt wheel pushes against the idler 22, which in turn pushes against the drive roller 20, thus creating a pressure contact between the capstan belt wheel 17 and idler 22, and between idler 22 and drive roller 20. A motor 24 causes rotation of the capstan drive roller 20. The roller 20 rotates idler 22, which in turn rotates wheel 17 so as to advance the tape 10.
In conventional capstan motor assemblies, the idler 22 may be supported on one end of a swinging link 22A so as to pivot about a pivot point 25 in a direction indicated by arrow A--A. The capstan motor 24, drive roller 20, and pivot point 25 may further be supported on a plate 27, which is also provided to pivot about a pivot point 31 in the direction of arrow B--B. Allowing the plate 27 and link 22A to pivot provides a substantially equal contact pressure between the drive wheel 20 and the idler 22, and between idler 22 and the capstan belt wheel 17.
Conventionally, at least the outer circular surface of idler 22 is covered with an elastic material having a high coefficient of friction. This material is provided to prevent slippage between the idler and the drive roller, and between the idler and the capstan belt wheel as those elements rotate in contact with each other. However, a problem with conventional capstan motor assemblies is that, over time, the circular surfaces of the capstan drive roller, the idler and/or the capstan belt wheel may become worn, and particulate matter may lodge between the elements, thereby deforming the circular shape of the elements. Moreover, dirt may accumulate on the elements, thereby decreasing the frictional force between adjacent contacting surfaces. All of these occurrences tend to cause slippage between the drive roller and idler, and between the idler and the capstan belt wheel. Slippage inhibits drive performance for several reasons. Significantly, it is very important to both monitor and control the speed with which the data tape advances past the recording area. When slippage occurs, there is no way to accurately control and maintain the speed of the advancing tape. Moreover, particularly during a recording cycle, the rotational speed of the capstan motor is often used to monitor the translational speed of the data tape. However, when slippage occurs, the motor speed will not accurately reflect the speed of the data tape. A loss of the ability to control and/or monitor the tape speed may result in read/write errors or even drive failure in extreme cases.